What Is a Drug Allergy?

A drug allergy is an allergic
reaction to a drug or medication. An allergic reaction means that your immune
system identifies the drug as foreign and acts to eliminate it from your body.
Your immune system responds to foreign substances in multiple ways, all of
which lead to increased inflammation. These inflammatory responses may cause
you to have symptoms such as rash, fever, or breathing difficulties.

True drug allergy is not common.
According to the World
Allergy Organization (WAO), it occurs in 3 to 5 percent of hospitalized
patients. Additionally, less than 10 percent of adverse drug reactions are
caused by genuine drug allergy.

Is A Drug Allergy Dangerous?

The symptoms of drug allergy
may be so mild that you hardly notice them. You might experience nothing more
than a slight rash. A severe drug allergy, however, can be life threatening. Anaphylaxis
is a sudden, severe, whole-body reaction to a drug or other allergen. It occurs
soon after exposure to the substance and includes symptoms such as irregular
heartbeat, difficulty breathing, swelling, and unconsciousness. If not treated
immediately, anaphylaxis can be fatal.

How Does Drug Allergy Work?

Your immune system is designed
to protect you from foreign invaders, such as viruses, bacteria, parasites, and
other toxic substances. When a drug enters your body, your immune system may
mistake it for one of these invaders. This might happen the first time you take
the drug, or it may not be until after you’ve taken it many times with no
problems.

As soon as the drug is
identified as a threat, your immune system begins to make antibodies. These are
special proteins programmed to attack just that one drug.

Some drugs, such as morphine,
aspirin, some chemotherapy drugs, and the dyes used in some X-rays, can cause
an anaphylaxis-type reaction the first time they are used. This does not
involve the immune system and is not a true allergy. However, the symptoms and
treatment are the same as for true anaphylaxis, and it is just as life
threatening.

What Is the Difference Between Side Effects and Drug Allergy?

A side effect is any secondary
action of a drug. It may be either harmful or beneficial. It is something that
might occur in any healthy person taking the drug and does not necessarily involve
the immune system.

For example, aspirin, which is
used to treat headache pain, often causes stomach upset (an adverse side
effect) and reduces your chance of heart attack and stroke (a beneficial side
effect); acetaminophen (Tylenol), which is used for pain, is associated with
liver damage (an adverse side effect); nitroglycerin, which is used to widen
blood vessels and improve blood flow, also improves mental function (a
beneficial side effect).

A drug allergy is a group of
symptoms caused by allergic reaction to a drug. An allergic reaction is the
result of response by your immune system.

What Is the Long-Term Outlook for Someone with Drug Allergy?

Your immune system can change
over time, and it is possible that your allergy will diminish or go away. However,
it could also get worse. If you have any symptoms of drug allergy or any side
effects to medication you are taking, discuss them with your doctor.

Mild allergic reactions to
drugs can usually be controlled with other medications to block the immune
response and reduce symptoms. Such medications may include:

antihistamines: These are drugs that calm symptoms of an
allergic reaction by blocking the production of histamine, a substance the
body produces in response to what it perceives as a harmful substance. The
release of histamine may trigger allergic symptoms such as swelling,
itching, or irritation.

corticosteroids: These help to reduce the inflammation that
may be causing swelling of airways and other serious symptoms.
Corticosteroids may be given orally, topically, or by injection.

bronchodilators: If you experience wheezing or coughing,
your doctor might recommend a bronchodilator. This will open the air
passages and make breathing easier.

If you have had a previous
allergic reaction to a drug, you should avoid using the drug in the future.
Your doctor will usually be able to use another drug to treat you.

In some cases, it may be
preferable to use the drug that you are known to be allergic to. If this
happens, you may be given antihistamines, corticosteroids, or bronchodilators
before taking the drug. This should only be done under close medical
supervision.

In some cases, you can be
desensitized to a drug. This involves repeated exposure to the drug. Your
doctor will start with a very low dose, which will be gradually increased until
you develop a tolerance. You should not try to do this on your own. The
procedure requires the close supervision of an allergist.

If you know that you are allergic
to any drug, be sure to inform all of your medical providers, including your
dentist and any other care provider who may prescribe medication. It is a good
idea to wear a bracelet or necklace or carry a card that identifies your drug
allergy—in an emergency, this could save your life.